DNA such as plasmids or naked DNA, and other vectors, such as viral vectors, e.g., vaccinia virus and more recently other poxviruses, have been used for the insertion and expression from foreign genes. The basic technique of inserting foreign genes into live infectious poxvirus involves recombination between pox DNA sequences flanking a foreign genetic element in a donor plasmid and homologous sequences present donor plasmid and homologous sequences present in the rescuing poxvirus (Piccini et al., 1987). Recombinant poxviruses are constructed in steps known as in or analogous to methods in U.S. Pat. Nos. 4,769,330, 4,772,848, 4,603,112, 5,505,941, and 5,494,807, incorporated herein by reference. A desire in vector development is attenuated vectors, e.g., for enhanced safety; for instance, so that the vector may be employed in an immunological or vaccine composition.
For instance, the NYVAC vector, derived by deletion of specific virulence and host-range genes from the Copenhagen strain of vaccinia (Tartaglia et al., 1992) has proven useful as a recombinant vector in eliciting a protective immune response against an expressed foreign antigen. Likewise, the ALVAC vector, a vaccine strain of canarypox virus, has also proven effective as a recombinant viral vaccine vector (Perkus et al., 1995). In non-avian hosts, both these vectors do not productively replicate (with some exceptions as to NYVAC). Since all poxviruses replicate in the cytoplasm and encode most, if not all of the proteins required for viral transcription (Moss 1990), appropriately engineered foreign coding sequences under the control of poxvirus promoters are transcribed and translated in the absence of productive viral replication.
It would be an improvement over the state of the art to provide enhanced vectors, e.g., vectors having enhanced transcription or transcription and translation and/or expression, for instance such vectors which are attenuated; especially since attenuation may raise issues of expression levels and/or persistence, and it would be an advancement to address such issues.